1. Field of the Invention
This invention relates generally to threaded connections adapted for use with oilfield pipe (xe2x80x9ctubularsxe2x80x9d). More specifically, the invention relates to threaded connections formed on downhole tubular members adapted to be plastically radially expanded in a wellbore.
2. Background Art
Casing joints, liners, and other oilfield tubulars are often used in drilling, completing, and producing a well. Casing joints, for example, may be emplaced in a wellbore to stabilize a formation, to protect a formation against elevated wellbore pressures (e.g., wellbore pressures that exceed a formation pressure), and the like. Casing joints may be coupled in an end-to-end manner by threaded connections, welded connections, and other connections known in the art. The connections may be designed so as to form a seal between an interior of the coupled casing joints and an annular space formed between exterior walls of the casing joints and walls of the wellbore. The seal may be, for example, an elastomer seal (e.g., an o-ring seal), a metal-to-metal seal formed proximate the connection, or similar seas known in the art.
In some well construction operations, it is advantageous to radially plastically expand threaded pipe or casing joints in a drilled (xe2x80x9copenxe2x80x9d) hole or inside a cased wellbore. In a cased wellbore, radially expandable casing can be used to reinforce worn or damaged casing so as to, for example, increase a burst rating of the old casing, thereby preventing premature abandonment of the hole. In open hole sections of the wellbore, the use of radially expandable casing may reduce a required diameter of a drilled hole for a desired final cased hole diameter, and may also reduce a required volume of cement required to fix the casing in wellbore.
Deformations proximate ends of radially expandable casing after radial plastic expansion are problematic when they are encountered proximate threaded tubular connections used on, for example, oilfield casing and tubing. Problems are encountered in at least three areas. First, internal metal-to-metal seals, which rely on radial contact stresses to form the seal, may unload if a pin nose formed on a pin connection deforms in a direction away from a seal surface formed on a box connection. Second, gross deformation of the pipe ends proximate the region of the threaded connection can cause some of the threads to move radially and, as a result, unload. This adversely affects a load carrying capacity of the threaded connection. Third, local deformations in the region proximate each individual thread may xe2x80x9ctwistxe2x80x9d the individual threads, thereby adversely affecting a load distribution between individual threads.
When a cold-forming expansion process is used (e.g., when a cold-forming expansion tool or xe2x80x9cpigxe2x80x9d is moved through a casing string so as to radially plastically expand the casing string), the casing string is usually run into the hole xe2x80x9cbox-downxe2x80x9d (e.g., the xe2x80x9cboxxe2x80x9d or female threaded connection is run into the hole facing downhole so that the expansion tool (xe2x80x9cpigxe2x80x9d) does not deform the pin nose of each connection when the expansion tool is forced upward through the casing string). Note that tubular strings such as drill pipe, casing, or similar tubular members are normally run into the hole xe2x80x9cpin-downxe2x80x9d because it is easier to make up the threaded connections in the tubular string.
Several problems have been encountered when attempting to maintain an effective internal pressure seal in threaded connections used with expanded casing strings. For example, elastomeric seals may be used in these applications, but a preferred internal pressure seal in oilfield applications includes a metal-to-metal pressure energized, gas-tight seal. Elastomeric seals impose limitations on the design the threaded connection itself, usually require specialized manufacturing techniques, impose limitations upon the materials that may be used, and do not provide the security of a true metal-to-metal seal.
Prior art analysis of expandable threaded tubular connections has concentrated on an analysis of the post-expansion stresses in the connection, with an implicit assumption that a relationship between stress and strain is relatively linear, even within the plastic deformation regime. However, thin-walled carbon steels typical of those used in oilfield tubular goods exhibit a drastically non-linear relationship between stress and strain during plastic deformation, particularly in a near-plastic region immediately following a yield point where plastic yielding is characterized by the formation of Lxc3xcders bands. For this reason, it is desirable that expandable threaded tubular connections be designed to control and focus the plastic strains resulting from expansion rather than be designed to achieve a desired stress field in the connection so that threaded connection and seal integrity may be maintained after radial plastic expansion of the threaded connection (and the associated tubular member on which the threaded connection is formed).
In one aspect, the invention comprises a radially expandable tubular connection. The radially expandable tubular connection includes a box member comprising an internal thread and a first seal surface and a pin member comprising an external thread and a second seal surface. The external thread is adapted to threadedly engage the internal thread and the first and second seal surfaces are adapted to form a metal-to-metal seal upon engagement thereof. At least one groove is formed on an outer surface of the box member, and the at least one groove is shaped so that the box member radially deforms in a direction toward the pin member axially proximate the metal-to-metal seal upon radial plastic expansion of the pin and box members after engagement of the threads.
In another aspect, the invention comprises a radially expandable tubular connection. The radially expandable tubular connection includes a box member comprising an internal thread and a first seal surface and a pin member comprising an external thread and a second seal surface. The external thread is adapted to threadedly engage the internal thread and the first and second seal surfaces are adapted to form a metal-to-metal seal upon engagement thereof. At least one groove is formed on an outer surface of the box member axially proximate the first seal surface, and the at least one groove is shaped so that the box member radially deforms in a direction toward the pin member axially proximate the metal-to-metal seal upon radial plastic expansion of the pin and box members after engagement of the threads.
In another aspect, the invention comprises a radially expandable tubular connection. The radially expandable tubular connection includes a box member comprising an internal thread and a first seal surface and a pin member comprising an external thread and a second seal surface. The external thread is adapted to threadedly engage the internal thread and the first and second seal surfaces are adapted to form a metal-to-metal seal upon radial plastic expansion of the pin and box members after engagement of the threads. At least one groove is formed on an inner surface of the box member, and the at least one groove is adapted so that the box member radially deforms in a direction toward the pin member proximate the seal surfaces after the radial plastic expansion.
In another aspect, the invention comprises a radially expandable tubular connection. The radially expandable tubular connection includes a box member comprising an internal thread and a first seal surface and a pin member comprising an external thread and a second seal surface. The external thread is adapted to threadedly engage the internal thread and the first and second seal surfaces are adapted to form a metal-to-metal seal upon engagement thereof. At least one pin groove is formed on an outer surface of the pin member between a last engaged thread and a pin nose, and the at least one pin groove adapted to reduce an amount of radially inward deformation of the pin member upon radial plastic expansion of the pin and box members after engagement of the threads.
In another aspect, the invention comprises a radially expandable tubular connection. The radially expandable tubular connection includes a box member comprising an internal thread and a first seal surface and a pin member comprising an external thread and a second seal surface. The external thread is adapted to threadedly engage the internal thread and the first and second seal surfaces are adapted to form a metal-to-metal seal upon engagement thereof. At least one substantially helical groove is formed on an inner surface of the pin member, and the substantially helical groove is positioned at substantially a same axial position along the pin member as roots of the external thread. The at least one substantially helical groove is adapted to reduce an amount of radially inward deformation of the pin member upon radial plastic expansion of the pin and box members after engagement of the threads.
In another aspect, the invention comprises a radially expandable tubular connection. The radially expandable tubular connection includes a box member comprising an internal thread and a first seal surface and a pin member comprising an external thread and a second seal surface. The external thread is adapted to threadedly engage the internal thread and the first and second seal surfaces are adapted to form a metal-to-metal seal upon engagement thereof. A plurality of circumferential pin grooves are formed on an inner surface of the pin member. Each of the plurality of substantially circumferential pin grooves is positioned at substantially a same axial position along the pin member as a root of the external thread, and the plurality of circumferential pin grooves are adapted to reduce an amount of radially inward deformation of the pin member upon radial plastic expansion of the pin and box members after engagement of the threads.
In another aspect, the invention comprises a radially expandable tubular connection. The radially expandable tubular connection includes a box member comprising an internal thread and a first seal surface and a pin member comprising an external thread and a second seal surface. The external thread is adapted to threadedly engage the internal thread and the first and second seal surfaces are adapted to form a metal-to-metal seal upon engagement thereof. At least one substantially helical groove is formed proximate a root surface of the external thread, and the at least one substantially helical groove is adapted to reduce an amount of radial deformation of the external thread upon radial plastic expansion of the pin and box members after engagement of the threads.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.